A fuel cell that is a main power supply source of a fuel cell system is a device that generates electricity through oxidation and reduction reactions of hydrogen and oxygen.
High purity hydrogen is supplied from a hydrogen storage tank to an anode of a fuel cell stack (hereinafter referred to as the “stack”), and air in the atmosphere, which is supplied by an air supply device such as an air compressor, is introduced into a cathode of the stack.
At the anode, the oxidation reaction of hydrogen takes place to generate hydrogen ions (protons) and electrons. The protons and the electrons are independently moved to the cathode through a polymer electrolyte membrane and a bipolar plate. In addition, at the cathode, the reduction reaction of the protons and the electrons from the anode with oxygen in the air supplied by the air supply device takes place, forming water and producing electrical energy due to the flow of the electrons.
Meanwhile, to purge hydrogen and discharge condensed water (condensate), a conventional fuel cell system includes a purge valve capable of selectively discharging hydrogen and other gases circulating in the anode to the outside, a water trap in which the condensate discharged from the anode is stored, and a condensate discharge valve capable of selectively discharging the condensate stored in the water trap to the outside. The purge valve and the condensate discharge valve may be also connected to a moist air discharge line discharging moist air discharged from the stack to the outside or a humidifier humidifying air to be supplied to the stack using the moist air. In this configuration, the hydrogen and other gases discharged from the purge valve and the condensate discharged from the condensate discharge valve may be discharged to the outside through the moist air discharge line.
When the hydrogen and other gases discharged from the purge valve are directly discharged to the outside through the moist air discharge line, the concentration of hydrogen in the exhaust gases is increased, thereby violating a regulation on the concentration of hydrogen in the exhaust gases. In addition, the hydrogen and other gases circulating in the anode, as well as the condensate, may be discharged through the condensate discharge valve. When the hydrogen and other gases discharged from the condensate discharge valve are directly discharged to the outside through the moist air discharge line, the aforementioned regulation may also be violated. In order to prevent the violation of the regulation on the concentration of hydrogen in the exhaust gases, the hydrogen purging and the condensate discharge may be performed in a state in which an air discharge valve disposed in the moist air discharge line is closed.
In addition, the moist air discharge line and the humidifier may be connected through the cathode to an air supply line supplying the air to the cathode, and the air supply line may be connected to a stack enclosure accommodating the stack therein by a vent pipe. Here, the vent pipe may be provided to transmit a negative pressure provided by an air compressor disposed in the air supply line to the stack enclosure. The gases leaking from the stack and contained in the stack enclosure may be sucked by the negative pressure provided by the air compressor, and be then discharged to the outside by sequentially passing through the vent pipe, the air supply line, the cathode, the moist air discharge line, and the like.
When power generation is stopped during the operation of the fuel cell system, the air compressor may be stopped. When the hydrogen purging and the condensate discharge are performed in a state in which the air compressor is stopped, the hydrogen may flow backward along the humidifier, the moist air discharge line, the cathode, and the air supply line, and may be introduced into the interior space of the stack enclosure through the vent pipe. In order for the conventional fuel cell system to diagnose whether the hydrogen discharged during the hydrogen purging and the condensate discharge flows back into the interior space of the stack enclosure or the hydrogen directly leaks from the stack into the interior space of the stack enclosure, it may be necessary to disassemble the stack enclosure and the stack. Thus, in the conventional fuel cell system, it may take a long time to diagnose whether the hydrogen discharged during the hydrogen purging and the condensate discharge flows back into the stack enclosure, and the assembly and disassembly of the stack enclosure and the stack may lead to a secondary failure.